Tree Black Growth and Sap: Gummosis from Borers or Black Knot Disease

Tree 1

Tree 2

New homeowner sees black growth on limbs with sap drips. Tree appears to be a fruit species.

Two Possibilities

1. Gummosis (Tree 2): Soft, gummy black sap = tree’s response to bark wound. Often caused by boring insects (peach tree borer, shothole borer). Sap flows from larval entry holes.
2. Black Knot (Tree 1): Hard, crusty, swollen galls on twigs = Apiosporina morbosa fungus. Common on Prunus. Spreads; kills branches if extensive.

Action

• Confirm tree ID (fruit type).
• For gummosis: inspect for borer holes; treat with Spinosad trunk spray.
• For black knot: prune galls 4–6" below swelling in winter; sterilize tools.
• Arborist visit recommended for accurate ID and prescription.